Worldwide production of isotactic polypropylene is based on contacting propylene with a catalyst based on a solid halogenated titanium compound, or a solid solution of halogenated titanium and halogenated organo aluminum compounds, which may be fixed by physico-mechanical processes or through chemical reactions on the surface of a support of a halogenated magnesium compound, usually in the presence of an electron donor compound, i.e., a Lewis base.
Though many other metallic elements have been suggested for use in catalysts for isospecific polymerization of alpha olefins, only the titanium catalyst is currently in commercial use because of its high yield of isotactic polymers. For example, various vanadium compounds such as vanadium acetylacetonate and vanadium tetrachloride, activated with diethylaluminum chloride and other similar compounds, have been shown to catalyze the polymerization of propylene at low temperatures to low molecular weight polymers rich in syndiotactic structures, but these polymers have inferior properties and are, thus, not industrially useful. However, these vanadium catalyst are currently in commercial use for the production of random ethylene/propylene and ethylene/propylene/diene elastomers.